Photoexcitation of tryptophan in aqueous solution at 280 nm is known to result in ionization with a quantum yield of 8% and in triplets with a yield of ca. 15%. The proposed experiment is aimed at the determination of the infrared spectrum in the 700-1700 cm-1 region with greatest interest in the 1400-1700 cm-1 region. The lifetime of the triplet state of tryptophan in aqueous solution ranges from 10 ?s for a solution degassed with argon to 1 ms for a rigorously deoxygenated solution. The lifetime of the radicals is on the order of ms. The pKa of the radical cation is 4.3 so in a pH 7 solution it will convert to the neutral radical by loss of the indole N-H proton. Measurements at both high and low pH are proposed to determine the spectra of both radical species and the time dependence of this acid-base reaction. The desired vibrational information is needed to demonstrate the feasibility and interpretability of similar experiments on proteins where ca. 100 ps time resolution is required.